1. Field of the Invention
The present invention relates generally to devices for assisting in achieving maximum sailboat speed to a given mark or destination, and more particularly pertains to computers which automatically, instantaneously and continuously calculate and display the magnitude of the velocity vector components of a sailboat so as to achieve maximum speed in reaching a mark.
2. Description of the Prior Art
It is a well understood fact that a sailboat cannot sail directly into the wind. In this respect, a sailboat at best can sail only about 20.degree. to the wind, and at such a heading, the boat's speed through the water is extremely low. As a sailboat "falls off" from the wind, its speed through the water increases, and a boat will reach its maximum speed through the water at about 100.degree. to 120.degree. to the wind, once again decreasing as it approaches a 180.degree. or downwind course. As such, most sailboat race courses are designed to have one of the "legs" of the course located directly upwind. Since a sailboat cannot sail directly upwind, a skipper or operator of a sailboat must choose some course "off" the wind that he thinks will get him to the windward mark in minimum time. In this regard, the skipper would like to attain the maximum "speed made good to the windward mark." However, it is almost impossible to determine the optimum direction, since if the angle is slightly too great, the boat will have a higher speed through the water but will be headed away from the mark at too large an angle so as to not attain the maximum "speed made good to the mark." Conversely, if the angle is too small, the boat will be headed nearer the mark but will have too low a speed through the water and still will not attain maximum "speed made good to the mark." As can be appreciated, the optimum speed-direction combination is the one that maximizes the algebraic product of the speed through the water and the trigonometric cosine of the angle between the direction to the mark and the direction of the speed through the water, i.e., the speed made good to the mark (SMG) is the projection of the velocity vector (V) onto the direct course and may be expressed as: EQU SMG=/V/Cos.sub..alpha.
where .alpha. is the angle between the sailing course and the direct course and /V/ is the magnitude of the velocity of the vessel. In this respect, the speed made good to the mark (SMG) is the component of the speed along the direct course.
As such, it can be appreciated that it is desirable to be able to determine the speed made good to the mark relative to various headings of the sailboat. Although the speed made good and the distance made good may be manually calculated using the speed of the vessel in the water (as read from a knotmeter), the compass reading and the direct course as inputs, such calculations are not readily available and do not permit prompt course corrections in order to maximize both the speed and distance made good. Effectively, the only manner of quickly combining the various parameters of calculate the speed made good is through the use of a computer. In this regard, there are already several sailboat computers on the market. However, they usually require a large amount of input information such as rhumb line direction (direction to the mark), relative wind speed, relative wind direction, and sailboat speed. Additionally, they require a lot of experimental input data, such as boat speed as a function of true and/or relative wind directions, plus different data associated for each of the sails contained in the sail inventory. These inputs are used to generate optimum course directions using rather sophisticated "on-board" computers and programs.
For example, U.S. Pat. No. 4,107,988, issued to Polsky, on Aug. 22, 1978, discloses a navigation aid for sailing vessels which provides a continuous indication of the actual progress towards a selected position, such as a course mark in a sailboat race. The actual progress is indicated in terms of speed made good and/or distance made good so as to enable immediate evaluation of the effect of course changes and variations in vessel performance. To accomplish this, the Polsky device senses the speed of the sailing vessel through the water and an output signal proportional thereto is obtained. Additionally, a sensor which is responsive to deviations from the direct course to the mark and which may be positioned in azimuth in accordance with that course is provided. The sensor is a Hall effect generator responsive to the earth's magnetic field, as well as to the output signal from the speed detector, and the sensor provides an output which is proportional to the product of the speed and the cosine of the angle between the course being sailed and the course to the mark. This output is utilized for the continuous indication of the speed made good by the vessel or may be integrated to indicate the distance made good, and effectively then, the Polsky device operates as a computer.
A similar type of course made good computing apparatus is to be found in U.S. Pat. No. 3,685,352, issued to Pounder et al, on Aug. 22, 1972, wherein the use of a gimbal-mounted magnetometer sensor for detecting the direction of the earth's magnetic field is disclosed. The magnetically sensitive axis of the sensor is aligned with the earth's magnetic field when the boat is headed on a desired course, and the sensor is then locked in a fixed position relative to the boat, with the magnetometer thereafter producing a voltage which is proportional to the cosine of the angular deviation of the boat from the desired course. A voltage signal representing boat speed is coupled with the voltage from the magnetometer in a multiplier to produce a voltage proportional to the vector component of the boat speed in the direction of the desired course. The voltage from the magnetometer sensor may then be fed to a meter to display the angular deviation of the boat from the desired course, and the voltage from the multiplier is fed to a meter to display the boat's velocity vector component in the direction of the desired course.
As opposed to utilizing the earth's magnetic field to sense course directions, U.S. Pat. No. 3,814,910, issued to Palmieri et al, on June 4, 1974, discloses a sailing computer for calculating the velocity made good during operation of a sailing boat by utilizing measured wind angle, wind speed and boat speed in an analog computer with a single multiplier and with linear relations thereout to provide an indication of velocity made good over the angle of sailing into the wind. In this respect, linear relations are substituted for trigonometric relations in the computer so as to present a solution algorithm utilizing the above-mentioned data sources.
As such, it can be appreciated that the use of sailing computers is desirable; however, such computers are severely hampered by the various types of inputs which must be obtained and supplied. Accordingly, it can be seen that it would be desirable to have a computer that would eliminate such inputs as wind speeds, wind directions (both true and relative) and sail characterization data to compute the optimum sailboat course direction. In this respect, the present invention substantially fulfills this need.